Thursday the country's Pollution Control Department said the concentration levels of PM 2.5, the tiny particles that measure air quality, had reached almost double the amount of concentrations considered safe.

Department officials blamed high humidity for contributing to the haze, while environmentalists cited the capital's famously traffic-choked streets.

Tara Buakamsri, Thailand director for Greenpeace Southeast Asia, in a Thursday Facebook post blamed Bangkok's polluted air on the city's abundance of cars and pollution from a coal-fired power plant in southern Thailand.

Many Bangkok commuters were seen sporting surgical masks, while some schools issued warnings over poor air quality and canceled outdoor activities.

Greenpeace also warned those living in other major Thai provinces over the poor air quality.

The Pollution Control Department said Wednesday that Thailand's northern region often sees haze from January to April, the country's dry season, as more forest fires occur and farmers burn materials to prepare for the impending rainy season. It said dry and still air traps dust particles and prevents them from falling to the ground, resulting in adverse environmental and health effects.

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